Re: [uCsimm] I2C

From: Geoffrey Wossum (
Date: Wed Oct 25 2000 - 14:31:17 EDT

> Does anyone know if ucsimm SPI port is compatible with
> I2C bus ?

No, you can't talk I2C over the SPI port. At the very least, you can't
get the SPI port to handle I2C ACKs, STARTs, STOPs, etc.

If all you need is an I2C master, and you don't mind wasting some CPU
power, bit banging off an I/O port is a possibility. Buffer the I/O port
through something like a 74LCX05, since exposing the I/O pins to 5 volts
will shorten their life, plus you need wired-OR for I2C. BTW, I've found
LCX parts work very well for isolating 3.3 and 5 volt sides of a circuit.
Plus their easy to find and inexpensive.

If you need slave support, you'll need to use a coprocessor, the uCsimm
couldn't cope otherwise.

I've had success with both I2C master and slave modes with the uCsimm
connected to a PIC16F877 based I2C coprocessor. One day, I'll actually
get around to making a webpage for the I2C coprocessor firmware. Probably
won't be until December, though.

Geoffrey Wossum
Project AKO -
Internet Imperialists -
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